I have a rear wheel, Westwood rim for 26" x 1 3/8" (37-590) from which I removed an old Raleigh tyre. I have a 37-590 Schwalbe Marathon tyre, the bead of which I cannot get to stay on. It's sibling tyre fitted perfectly on the front wheel. The tyres aren't new but still have spiky bits from the moulding
How do I get it to play nicely?